Typically, a book comprises a plurality of sheets with printed pages, stacked on one another and which constitute a block book, and a cover bounded with the block book. In manufacturing systems for books “on demand”, the printing is performed on both sides of a continuous paper strip and defines book sections in sequence. Each book section is associated to a book and is different from the preceding and the following section in the case of books with different titles. The paper strip is of origin for basic sheets of the block book, which are separated by transversal cuts and, possibly, by longitudinal cuts and are processed individually in operations of stacking and preparation of the block books, subsequently trimmed. The above mentioned manufacturing systems allow to process customer orders quickly and efficiently, with fidelity to the original editing of the books but, ceteris paribus, the operating speed of the system is negatively affected by the number of transversal cuts on the continuous strip.
According to an editorial technique by signatures and specific editing, the basic sheets of a book are derived from “signatures” obtained, by folding, from respective signature sheets. By way of example, a signature in 8° corresponds to a transversal fold in a half of a signature sheet, followed by a longitudinal fold. A signature in 12° corresponds to a transversal fold in a half of a signature sheet, followed by two zig-zag longitudinal folds. Signatures in 16° and in 24° can be obtained with a second fold. In the lines of the folds, the sheets of the books are then separated in a trimming step. This technique by “signatures” allows to obtain book blocks with ease and a number of loose sheets reduced with respect to the number of sheets required to form the same basic block with basic sheets cut individually.
The technique by signatures can be applied to produce books, specifically, but not exclusively “books on demand” with printing on a continuous paper strip. The paper strip maintains the configuration of book sections arranged in sequence: each book section is constituted by signature sheets, each formed with a predetermined number of basic sheets, while the number of signature sheets depends on the number of pages in the book. The transversal cuts required for the basic sheets are reduced, resulting in a greater speed of the system.
In particular, the continuous paper strip is processed by a book manufacturing system, which includes a transversal cutting equipment for cutting the strip and separating the basic sheets, in groups, as signature sheets and a transversal folding equipment for transversally folding the separated signature sheets. A longitudinal folding equipment folds longitudinally the previously folded signature sheets, forming respective signatures and a stacking and gluing device stacks then the signatures, forming a basic book block for subsequent treatments.
For manufacturing books “on demand” by signatures of the above defined type, and fidelity to the original editing of the printed pages, the last signature of the book block, and the finished book can be constituted by a large number of blank pages. This, in addition to constitute a waste of paper, is not considered favorably by the editorial market.
On the other hand, the formation of signature sheets with a smaller number of basic sheets, for example by forming the signatures only with a row of flanked basic sheets, would increase the number of transversal cuts, giving rise to a consequent reduction of the operating speed of the system.